Hydraulic circuit breaker with dual series piston actuation



HYDRAULIC CIRCUIT BREAKER WITH DUAL SERIES PISTON ACTUATION Filed May 25, 1962 NI q om m mm UN -illwnfl m m m N Nm O ut 21 ON W Q .wo N i w. 9 4. 9 ZmaO Oct. 12, 1965 p DUFFING ETAL 3,211,851

HYDRAULIC CIRCUIT BREAKER WITH DUAL SERIES PISTON ACTUATION 3 Sheets-Sheet 3 Filed May 25, 1962 m mm .mm Nv om .v n v mm mm mm mm lclll .m .mn B ---I n n u n w n 4 O w i--- .omv ...mm .N omm sm mm .m .ai

United States Patent O 74,116 7 Claims. '(Cl. 200-82) This invention relates generally to hydraulically operated circuit breakers and, more particularly, to an improved hydraulically operated circuit breaker in which a series double-piston device is utilized for etfecting actuation Of the circuit breaker.

A general object of the present invention is to provide an improved hydraulically Operated circuit breaker in which the energy losses are reduced to a minimum in the transmission of hydraulic fluid through the lines to the hydraulic mechanism.

Another object of the invention is to provide an improved hydraulic mechanism for a circuit breaker in which a double series piston device including pistons of different cross sectional areas, movable in Operating cylinders of different cross sectional areas, are employed for moving the movable circuit breaker contact to one Of its two positions, namely the closed position Or to the open position.

Yet a further object of the present invention is to provide a Variable hydraulically actuated damping device for a circuit breaker in which a series double piston hydraulic device is utilized.

Still a further object of the present invention is to provide an improved hydraulic mechanism for a circuit breaker in Which one hydraulic device effects the opening of the circuit breaker and a second hydraulic device effects the closing of the circuit breaker.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in Which:

FIGURE 1 illustrates a hydraulic Operating mechanism connected to a circuit breaker (diagrammatically illustrated), the device being illustr-.aited in the open circuit position;

FIG. 2 is a modified type of hydraulic circuit interrupter mechanism, again the several parts being illustrated in the open circuit position; and

FIG. 3 illustrates a further modified type of circuit breaker hydraulic Operating mechanism in which separate hydraulic devices are utilized for etfccting both the open and closing operations of the breaker, the several parts being illustrated in the closed circuit position.

As well known by those skilled in the art, hydraulic Operating mechanisms have previously been used for circuit breaker applications. In general, such hydraulic operating mechanisms comprise a piston Which moves Within an Operating cylinder. As is usual, the hydraulic piston is moved by a pressurized Operating fluid, such, for example, as pressurized hydraulic oil. As is usual, the piston is connected by suitable linkage to the circuit breaker shaft, preferably by means of a crank arm- It is well known that it is desirable to effect quick operation of circuit b-reakers. Therefore, there is generally not used a pump for supplying the pressurized hydraulic liquid, such, for example, as hydraulic oil, into the operating cylinder; but there is preferably provided for the supply of the pressurized hydraulic fluid into the cylinder 3,21 1,851 Patented Oct. 12, 1965 an energy accumulator, which is slowly charged by a hydraulic pump. Such an energy accumulator may consist, for example, Of a fluid filled container in Which there is a gas Which is compressed under pressure.

For fast operation of circuit breakers, the moving masses must be rapidly accelerated at the beginning of the movement and at the end of the movement they must be correspondingly decelerated. For this purpose, a constant pressure in the Operating cylinder of the known hydraulic leakage systems is not suitable, because it would provide the desired acceleration of the moving masses not only at the beginning of the travel, but also it would accelerate the moving masses further along during the entire course of the travel. Therefore, there is usually built into the pipe line, Which brings the hydraulic fluid from the accumulator into the Operating cylinder, a throttle (or, in certain cases, the cross sectional area of the pipe line is reduced cO-rrespondingly) so that the pressure in the operating cylinder decreases with the increase of speed of the Operating piston. In this Way it results tha-t the pressure and, therefore, the force On the piston decreases at the end of the travel, and that devices necessary for braking, or for decelera-tion, of the masses at the end Of the travel do not need to be too large. The passage of the hydraulic fluid through the throttle causes an energy loss, which must be provided by the accumulator.

According to the present invention, this energy loss can be prevented by a construction in which two pistons of different cross-sectional areas and Operating within corresponding dimensioned Operating cylinders are used as the hydraulic linkage system, and preferably one of the pistons is directly connected with the Operating cylinder associated With the other piston. During the first portion of the movement of the circuit breaker, the piston having the larger diameter is moved so that a large initial acceleration is obtained. Following complction of its stroke, the small piston, which provides Only the small work for complction of the breaker travel, moves. In this Way, there is obtained the desired dependency of the force acting upon the moving masses Without the throttling Which has been previously necessitatcd in the case of known hydraulic drives. Whereas in the case of known hydraulic drives for each unit of length of the piston travel, there always occurred the same volume of hydraulic liquid taken from the accumulator, in the case of the hydraulic linkage system according to the present invention after the end of the travel Of the larger piston, Only a relatively small volume of hydraulic liquid is consumed for eachl unit of length of the piston travel. But, smaller volume consumption means at the constant pressure of the accumulator a smaller energy consumption.

It is of additional advantage, When the piston Which is connected to the cylinder of the other piston forms With this a -single piece. Preferably, this piston can be provided with an axial running borc which forms the cylinder for the Other piston. This has a distinct advantage in requiring only one inlet to be provided.

A hydraulic linkage system may be utilized for effecting -the closing Operation of the circuit interrupter, and for effecting the opening operation there may be used either an accelerating spring Or a hydraulic linkage system. For this purpose, in the pipe line to the sump of the energy .accumulator there is provided a throttle. This is of advantage in that at the return travel Of the hydraulic linkage at the beginning of movement only a small throt- .tling action will take place; then only the small piston returns at first and, consequently, only a small quantity O-f oil flows through the small cross-sectional area of the throttle. When the larger piston returns at the end Of the travel, a correspondingly larger volume of hydraulic liquid must flow through the throttle, and a correspondingly large throttling action occurs. Thus, this throttle substitutes for the otherwise customarily used throttling, or damping devices, such as oil pumps, friction brakes, etc. This is especially of advantage when the hydraulic linkage according to the present invention is used for opening as well asY for closing operations, because then always one linkage system ac-ts as a damping, or throttling, device of the movement provided by the other linkage system which at the beginning is only insignificant, but toward the end of the movement is as large as is desired.

The hydraulic Operating linkage system of the present invention is particularly suitable in connection with an accumulator in which the accumulator tank is completely filled with the pressurized hydraulic liquid, i.e. the accumulator contains no gas and the storage of energy takes place due to the compressionof the hydraulic liquid and also by the elastic expansion of the accumulator tank.

Referring to the drawings, and mor-e particularly to FIG. 1 thereof, the reference numeral 1 generally designates a hydraulically actuated circuit interrupter comprising a relatively stationary contact 2 and a cooperable separable movable -contact rod 3. Preferably a line connection L1 is suitably connected by a connector 2a to the stationary contact 2 and a second line connector Lz is electrically connected by a flexible connector 5 to the movable contact 3 of the circuit breaker contact structure, generally designated by the reference numeral 6. As shown in FIG. 1, the diagrammatically illustrated movable contact 3 is connected by an insulating extension Sa to an Operating crank arm 8 by means of a pivot pin 9. The crank arm 8 is rotatable with an Operating shaft 10 and is m-ovable between an opening stop 11 and a closing stop 12.

A pivotally mounted latch device 14 rotatable about a fixed pivot axis 15 is biased in a latching direction by a tension spring 16 and is released from engagement-with a dog 17 movable with the breaker shaft 10 by the energization of a latch release device 18. The energization of the latch release device 18 is effected by closing an opening push button 19 which effects through a battery circuit 20 energization of the coil 21 of the device 18 and hence counterclockwise rotative releasing movement of the latch 14.

To eflect opening operation of the circuit breaker, preferablyrthere is provided an accelerating spring 23 which is secured at one end 24 to the extremity of the crank arm 8. The other end of the accelerating spring 23 is Secured to a fixed support bracket 25.

As shown in FIG. l, an accumulator 26 is provided containing a suitable pressurized hydraulic liquid, such as oil 27. In addition, a sump 28 is provided to furnish hydraulic liquid through a pump 29 to be injected through a unidirectionally acting valve 30 and to the accumulator chamber 26. A sump line 31 having a control valve 32 and a restriction 33 is provided leading to the inl-et 34 of a T connection 35. The branches of the T connection 35 leads through flexible conduits 36, 37 to the respective ends of the relatively large Operating cylinder 38 and to a relatively small Operating cylinder 39.

i It will be noted that the relatively large Operating cylinder 38 s fixedly .secuned by bolts 40 to the relatively small Operating piston 41 movable withinthe bore of Operating cylinder 39. The relatively :small Operating cylinder 39 is pivotally connected about a pivot axis 42, v

the latter journalled upon a stationary mounting bracket 43.

' To control the admission of pressurized hydraulic liquid out of the accumulator 26 and into the conduit system 36, 37, preferably there is provided an accumulator control valve 44.

* As will be apparent from the foregoing description, the hydraulic linkage 45 generally comprises a piston 46 associated With. a. correspondingly enlarged Operating cylinder 38. In addition, the hydraulic linkage 45 consists of a series device comprising a hydraulic piston 41 of smaller diameter movable within a correspondingly small- -er diameter op'erating cylinder 39. It will be noted that relatively enlarged Operating cylinder 38 has a stroke limiting stop 47. In addition, as mentioned, the relatively enlarged Operating cylinder 38 is fixedly Secured and movable with the relatively small hydraulic piston 41. For the purpose of supplying both cylinders 38, 39 with pressurized oil there are provided the two flexible conduits 36, 37. Both of these flexible conduits 36, 37 are connected at one end with the accumulator 26 through a pipe line 48. The flexible conduits 36, 37, on the other hand, are connected to the sump 28 through the pipe line 31 and valve 32. As shown, the sump line 31 is provided with a throttle 33, or, in the alternative, the cross sectional area of the sump line 31 may be correspondingly reduced. The sump 28 is connected in a known manner through the pipe line 49 to the pump 29 and through the supply line 50 past the valve 30 to the pressurized accumulator chamber 26.

As shown in FIG. 1, the circuit breaker shaft 10 is rotatable by means of the Crank arm 8 with which the piston rod 51 is connected by means of the pivot pin 52. The Operating cylinder 39 swivels about the stationary pivot pin 42. The accelerating spring 23'tends to eflect opening of the circuit breaker 1 but the latch 14 maintains the closed position thereof until released by actuating the Opening button 19. The operation of the hydraulic mechanism 45 Will no be described. To eitect the closing operation of the circuitinterrupter 1, the. control valve 44 is opened and the control valve 32 leading to the sump 28 is closed. After opening the control valve 44, the larger piston 46 moves toward the left within its larger diameter Operating cylinder 38 up to the limiting stop 47. As a result, such action accelerates with considerable force the movable masses and partially extends the accelerating spring 23,

which is completely stretched when the breaker is in the.

fully closed position. After the movement of the operating piston 46 has been completed within the larger diam- Operating cylinder 38 and the piston 46 are carried along and conclude the closing travel Of the crank arm 8 with a.

smaller force and at the same time stretching the spring 23 to a further extent. are latched in the closed position by latching of the nose 1411 of latch device 14 against the .surface 17a of dog 17 aflixed to the Operating shaft 10. The breaker is, as a result, latched in the closed circuit position, indicated by the dotted lines 53 in FIG. 1 of the drawings.

' To effect the opening operation the valve 44 is closed, the valve 32 is opened, and the latch release device 18 is energized by. closure of the opening push button 19, or by suitable equivalent means. As a result, the latch 14 is released and accelerating spring 23 pulls the crank arm 8 in a counterclockwise opening direction about the breaker shaft 10 affecting Opening of the Contacts 2, 3 to the open circuit position shown by 'the full lines in FIG. l. At the same time, the small piston 41 moves within small diameter Operating cylinder 39 to the right and takes along therewith the larger cylinder 38. During this initial opening movement the piston 46 does not move relatively to the larger Operating cylinder 38. As a result, only a small quantity of oil is forced through the throttle restriction 33 by the piston 41. At the end Of the opening movement of the piston 41, the latter strikes the stop 54 of the cylinder 39. When this occurs, the larger piston 46 moves toward the right within Operating cylinder 38 to the indicated position shown in FIG. l. At the same time, a much larger quantity of hydraulic liquid is forced through the throttle 33 and into the sump 28, due to which a considerable damping, Or slowing down, of the opening movement of the breaker parts during the latter part of the opening travel is obtained, Which is desirable.

The circuit breaker Contacts 6,

a welded on cover 26a and a welded on bottom plate 26b. It is completely filled with |oil and has at its upper location an opening, closed with .a screw plug 55, through which the air may escape when the container 26 is being filled initially with oil. The container is connected with the oil pump 29 through the check valve 30. The former is set into operation when the pressure within the energy accumulator falls below a preferred value, and it stops working when the normal pressure within the accumulator 26 is again attained.

As an alternative construction, not shown in FIG. 1, the entire series double piston device 56 may be reversed from the position shown in FIG. l and the operating cylinder 39 pivotally connected to the pivot pin 52, whereas the piston rod 51 could be pivotally connected to' the stationary pivot pin 42. The operation in such a transposed position of the parts would be identical to that hereinbefore described.

FIG. 2 illustrates the modification of the invention in which the relatively large 1Operating cylinder 38 swivels upon the pivot pin 42. 'Il-he large piston 46 and the small cylinder 39 constitute one unitary piece. Small operating piston 41 is hinged to pivot pin 52 on the crank arm 8. The relatively small piston 41 has a stop 54a. The large cylinder 38 is provided with a stop 47a. The remaining parts correspond to those set forth in FIG. l of the drawings and are consequently labeled with the same reference numerals. In the modification according to FIG. 2, during the closing operation at first the relatively large piston 46 moves within the relatively large yOperating cylinder 38 until its movement is limited by the stop 47a. The accelerating force is transmitted through the cylinder 39 and the stop 54a to the drive pin 52. After the relatively large piston 46 has -stopped at the stop 47a, the relatively small piston 41 moves toward the left Within 'Operating cylinder 39, which now is stationary and completes the closing movement With a relatively small force. During the opening sequence, first the small piston 41 moves within Operating cylinder 39 and then the large piston 46 moves within relatively large operating cylinder 38. The manner of operation is the same as that set forth in the arrangement according to FIG. 1.

As was the case With the inversion of the parts suggested in FIG. 1 of the drawings, also in the case of the embodiment of FIG. 2, the piston 41 may be pivoted upon stationary pivot pin 42, whereas the relatively enlarged Operating cylinder 38 may be hinged upon the drive pin 52 secured to the crank .arm 8. There would, in accordance with such an inversion iof the parts, be no change in the manner of operation.

FIG. 3 illustrates a further modification of the present invention in which a separate hydraulic device or operator is utilized to effect opening of the circuit breaker, whereas a second hydraulic device or operator is utilized to effect closing of the circuit breaker. In the arrangement according to FIG. 3, the piston 46' is stepped off and is provided with a bore 39' running throughout its length. This bore 39' provides a surface upon which the relatively small piston 41' slides. This piston 41' is provided with a collar 41. The Operating cylinder 38', within which the piston 46' moves, has a stop 38" and is pivotally mounted upon pivot pin 42', which is stationary. Relatively small Operating piston 41' pivots upon drive pin 42' of a double armed lever 8'. Two stops 12', 11' limit the closing and opening movement, respectively, of the double arm lever 8'. There is provided only one flexible inlet connection 57, which is connected through a pipe line 58 including a valve 59 with the accumulator 26. The flexible inlet connection 57 is also connected through a pipe line 58 including a valve 61 to the sump 28.

To the other end of the rotatable double armed lever 8' is connected a hydraulic linkage system which is built upon the same principle. The corresponding parts are labeled with the same figures except that they are pro- 6 vided with a suffix a. One linkage closes the breaker; the other linkage effects its opening operation.

In order to hold the circuit breaker in either of the two end positions, there is provided respectively a stop lever 64 cooperable lwith a notch 65. The stop lever 64 swivels .about a stationary pivot pin 66 and is biased in a latching direction by a tension spring 67. Similarly, there is provided a stop lever 70 cooperable with a latch 71 and rotatable about a fixed axis 72, being biased in a latching direction by a tension spring 73.

When the double arm lever 8' is moved from the closed position shown toward the other position, the valves 59, 61a are opened, whereas valves 61, and 5911 are closed. As a result, hydraulic pressurized liquid flows from the accumulator 26 through the pipe line 57 and into the large cylinder 38'. As a result, the relatively large piston 46' moves toward the right and after opening the latching device 64 by camming action, the lever 8' is rotated with it. At the same time, the relatively small piston 41a' in the relatively small cylinder 4611' is pushed inwardly. The small volume of oil, which thus flows through the throttle 33a into the sump 28, has only an insignificant throttling, or damping effect, so that the force produced by the piston 46' is available almost entirely for the acceleration of the moved masses of the breaker. During the further progress of the movement, the large piston 46' strikes the stop 38" and then the small piston 41' moves within the cylindrical bore 39' of the relatively large piston 38' in the opening direction, Whereby only a small force is transmitted to the breaker shaft 10'. When during the course of movement the stop 41a" comes into contact with the large piston 46a', then the latter will be pushed into the cylinder 38:1'. As a result, a large quantity of oil is forced through the throttle 33a into the sump 28, and it will result in la considerable throttling or damping action. The movement of the breaker will, consequently, be cons-iderably slowed down or dampened, but it will continue to progress toward the opening position until the double arm lever 8' strikes the stop 70. When the Stopping latch 70 falls within the recess 71, the valves S9, 61a Will be closed.

During the closing operation of the circuit interrupter illustrated in FIG. 3, the valves 5911 and 61 are opened and the upper hydraulic linkage moves in the closing direction. First, the large piston 4611' and then the small piston 41a' will move. Cons-idering the lower hydraulic linkage, first the small piston 41' Will move and subscquently the lar-ge piston 46' will move. The manner in which this operates is corresponding to that which was described previously for open-ing.

It will be readily apparent to those skilled in the art Ithat the diameters of the pistons and their strokes are so selected that the desired speed of operation is obtained. As a result, the stroke of the pistons of one hydraulic system can be selected different in length and also in stroke and the diameter of the pistons of the other system can be selected differently from those of the first system. The choice depend-s upon the requirements set forth for the closing and opening operation.

From the foregoing description of three embodiments of the invention, with two suggested inversions of the linkages of FIGS. 1 .and 2, it will be apparent that there is provided Ian improved serially related double acting piston hydraulic mechanism suitable for minimizing the energy losses and for effecting a desired damping operation during the stroke of a circuit breaker at which it is desired.

Although there has been illustrated and described specific Structures, it is to be clearly understood that the same were merely for the purpose of illustration and that changes and modifications may readily be made therein by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A hydraulically-operated circuit breaker including a pair of separable contacts, at least one of which is movable to an open position and to a closed position, a hydraulic linkage including first and second pistons and Operating cylinders of differentcross-sectional area moving said one movable contact to One of its two positions, means mechanically connecting the Operating cylinder of one -piston to the other piston, an accumulator, hydraulic passage means including an inlet valve for supplying hydraulic fluid under pressure to said first and second operating cylinders, a sump, additional hydraulic passage means including an exhaust valve for exhausting hydraulic fluid from said first and second Operating cylinders, whereby operation of said inlet and exhaust valves effects opening and closing movements of said one movable contact.

2. A hydraulically-operated crcuit breaker including a pair of separable contacts, at least one of Which is movable to an open position and to a closed position, an accelerating spring connected to said one movable contact to bias the same to the open position, ahydraulic linkage including first and second pistons and Operating cylinders Of different cross-sectional area moving said one movable contact to one of its two positions, means mechanically connecting the Operating cylinder of one piston to the other piston, an accumulator, hydraulic passage means including an inlet valve for supplying hydraulic fluid under pressure to said first and second Operating cylinders, a sump, additional hydraulic passage means including an exhaust Valve for exhausting hydraulic fluid from said first and second Operating cylinders, whereby operation of said inlet and exhaust valves effects Opening and closing movements of said One movable contact, and means providing a restriction in said additional hydraulic passage means to provide a desired damping action at the end of the opening operation.

3. A hydraulically-operated crcuit breaker including a pair of separable contacts, at least one of which is movable to an open position and to a closed position, a hydraulic linkage including first and second pistons mechanically connected in series and Operating cylinders of different cross-sectional area moving said one movable contact to one of its two positions, means mechanically connecting the Operating cylinder of One piston to the other piston, an accumulator, hydraulic passage means including an inlet valve for supplying hydraulic fluid under pressure to said first and second Operating cylinders, a sump, additional hydraulic passage means including an exhaust valve for exhausting hydraulic fluid from said first and second Operating cylinders, whereby operation of said inlet and exhaust valves effects opening and closing movements of said One movable contact.

4. A hydraulically-Operated crcuit breaker including a pair of separable contacts, at least one of Which is movable to an open position and to a closed position, a breaker Operating shaft, a crank arm connected to said One movable contact and affixed to said breaker operating shaft to cause the Opening and closing motion thereof, a hydraulic linkage including first and second pistons and Operating cylinders of different cross-sectional area moving said one movable contact to One of its two positions, means mechanically connecting the Operating cylinder of 'one piston to the other piston, the piston of smaller crosssectional area being directly connected to a pivot pin on said crank arm, an accumulator, hydraulic passage means including an inlet valve for supplying hydraulic fluid under pressure to said first and second Operating cylinders, a sump, additional hydraulic passage means including an exhaust valve for exhausting hydraulic fluid from said first and second Operating cylinders, whereby operation of said inlet and exhaust valves effects Opening and closing movements of said one movable contact.

5. A hydraulically-operated circuit breaker including apair of separable contacts, at least one of which is movable to an open position and to a closed position, an accelerating spring connected to said one movable contact to bias the same to the open position, a breaker Operating shaft, a crank arm connected to said one movable contact and afiixed to said breaker Operating shaft to cause the opening and closing motion thereof, a hydraulic linkage including first and second pistons and Operating cylinders of different cross-sectional area moving said one movable contact to One of its two positions, means mechanically connecting the operatnig cylinder of one piston to the other piston, the piston of smaller crOss-sectional area being directly connected to a pivot pin on said crank arm, an accumulator, hydraulic passage means including an inlet valve for supplying hydraulic fluid under pressure to said first and second Operating cylinders, a sump, additional hydraulic passage means including an exhaust valve for exhausting hydraulic fluid from said first and second Operating cylinders, whereby operation of said inlet and exhaust valves effects opening and closing movements of said one movable contact, and means providing a restriction in said additional hydraulic passage means to provide a desired damping action at the end of the Opening operation.

6. A hydraudically-operated crcuit breaker including a pair of separable contacts, at least One of which is movable to an open position and to a closed position, a breaker Operating shaft, a crank arm connected to said one movable contact and aiiixed to saidV breaker Operating shaft to cause the opening and closing motion thereof, a hydraulic linkage including first and second pistons and Operating cylinders of different cross-sectional area moving said one movable contact to one of its two positions, means mechanically connecting the Operating cylinder of one piston to the other piston, the piston of larger cross-sectional area being directly connected to a pivot pin On said crank arm, an accumulator, hydraulic passage means including an inlet valve for supplying hydraulic fluid under pressure to said first and second Operating cylinders, a sump, additional hydraulic passage means including an exhaust valve for exhausting hydraulic fluid from said first and second Operating cylinders, wher'eby operation of said inlet and exhaust valves effects opening and closing movements of said one movable contact.

7. A hydraulically-operated circuit breaker including a pair of separable contacts, hydraulic means for moving one of said contacts to be open and closed-crcuit positions, said hydraulic means including a first hydraulic operator having first and second pistons and Operating cylinders of different cross-sectional area for moving said one movable contact to one of its two positions, means mechanically connecting the Operating cylinder of one piston to the other piston, said first hydraulic operator effecting opening of said one contact, said hydraulic means including a second hydraulic operator having first and second pistons and Operating cylinders of different cross-sectional area for moving said one movable vcontact to One of its two positions, means mechanically connecting,

References Cited by the Examiner UNITED STATES PATENTS 2,773,484v 12/56 Peek 91-355 2,920,607 1/60 Barkan 91-469 BERNARD A. GILHEANY, Primary Examiner. 

1. A HYDRAULICALLY-OPERATED CIRCUIT BREAKER INCLUDING A PAIR OF SEPARABLE CONTACTS, AT LEAST ONE OF WHICH IS MOVABLE TO AN OPEN POSITION AND TO A CLOSED POSITION, HYDRAULIC LINKAGE INCLUDING FIRST AND SECOND POSTIONS AND OPERATING CYLINDERS OF DIFFERENT CROSS-SECTIONAL AREA MOVING SAID ONE MOVABLE CONTACT TO ONE OF ITS TWO POSITIONS, MEANS MECHANICALLY CONNECTING THE OPERATING CYLINDER OF ONE PISTON TO THE OTHER PISTON, AN ACCUMULATOR, HYDRAULIC PASSAGE MEANS INCLUDING AN INLET VALVE FOR SUPPLYING HYDRAULIC FLUID UNDER PRESSURE TO SAID FIRST AND SECOND OPERATING CYLINDERS, A SUM, ADDITIONAL HYDRAULIC PASSAGE MEANS INCLUDING AN EXHAUST VALVE FOR EXHAUSTING HYDRAULIC FLUID FROM SAID FIRST AND SECOND OPERATING CYLINDERS, WHEREBY OPERATION OF SAID INLET AND EXHAUST VALVES EFFECTS OPENING AND CLOSING MOVEMENTS OF SAID ONE MVABLE CONTACT. 